Microphone with opposite electrodes being of varying and constant curvature



Dec. 5, 1950 R. R. STEVENS 2,532,741

MICROPHONE WITH OPPOSITE ELECTRODES BEING OF VARYING AND CONSTANT CURVATURE Filed Oct. 31, 1947 lNl/ENTOR By R. R. STEVENS A T TOR/VEY Patented Dec. 5, 1950 PATENT" OFFICE MICROPHONE. WITH' OPPOSITE. ELEC- TRTODES, BEING. OF" VARYINGQ AND CONSTANT"CURYATURE" Ralplr. m". Stevens; Ghathamg- N2 J1, assi'gnorz to; Bellu'lelenhonerhabcratories;,Incorpprated,,New YnrkaNnY ,a.- corporation of New York Applicatiomactober '31, 1943, Slfiit-IKNO: 783E239 83-:Claims. 1,-

This invention relatesto telephone. transmitters and more particularl3r-= to" carhon granule type transmitter unitsespecially suitablefor use in hand telephones;

One general object of'this invention is-to -im prove the operatingcharacteris'tics -of-" telephone Moreliam L. Tufinell comprisesa'pair'ofi coaxial'idished electrodes and associated elements" huun'diirg a, carbon" granule chamber; one of the: electrodes being fixed. and the-other being-coupled to a diaphragm" to vibrate therewith.

In" accordancewith one' feature .Of invention; the surfaceof' one-of the electrodes is a. surface ofrevolution' the" generat'rix "of "whichis:

of" continuously varying curvature andv the" surface" of' the other: electrode also is one' of'revoluthan having, a generatrix-of constant. curvature. The two surfacesare coaxial and "inj uxtaposition and because of the difierencejn' the configura tions, of thesesurfaces the gap therebetween varies continuously so that for each position in which the unitmaybeheldan-optimum or substantially optimum current path between the two electrodesobtains Also because" of the difference, the spacing between the-two: electrodes may be madez quite small whereby improved modulation is obtained.

The invention and the above-noted and. other: features thereofwill'beunderstood; more. clearly. and fully; from the following detailed description; with: referenceto the accompanying drawing-in, which? Fig. Us a side'view insectionofla transmitter; unit'illustrative ofone embodimentlof this ,inven'-- tion; and

Fig. 2 is a fragmentary sectional view illustrating a modification of the unit shown in Fig. 1.

Referring now to the drawing, the transmitter unit illustrated in Fig. 1 comprises an annular, metallic foundation member or frame l having a cylindrical portion ll of reduced diameter and having also a plane face against which the annular peripheral portion 12 of a diaphragm is seated. The diaphragm, which may be formed in one piece of light weight metal, includes a central frusto-conical part I3 provided with stifiening corrugations'or'flutes I4 and: connected;

to the peripheral portion: r2 by an. annular" cor rugated or: trough portion l5? whichiis sufficientlyflexible: to allow: lbodilyi vibration. of i the: centralpart l3. The diaphragm, together withamoisturei-prootifmembrane. l6 and aimultt-apertured protectivezcoven'or 'screen I1; is. secured to;

frame by a. clamping band l8;

Mounted hythe diaphragmaand .v-ibratiletherewith is an electrode IQ of 'para-boloid'all' form and having a flange 28 and tabs 2! between which the' inner" edgeportion: of the' diaphragm isgripped; Al'sosecured between the flange and tabs are' the-=inner portions of" a metallic. spider 22' and'an annular; flexible closure member 23;

for example of silk. The arms" of the spider, which serves-res alead in conductor tothe electrode-- l9, extend-toand contact an inner, annular-flange 24on'theioundation member or frame The outer portion of the closure member 23 is held between a pair of insulating'rings 25' and26 withirrthe cylindrical portion H 0fthe foundation memo'er; thering 26"being seated upon an insulatingspacer 2-1 which inturn bears against the spider arms:

A fixed electrode-is mounted upon the ring 25' and comprises an annular flange 28' seated on'this ring, anda central domed part having a hemispherical surface 29 in juxtaposition toand coaxial with the paraboloidal electrode I91 The" fixed electrode is provided with" an aperture 30 through which a-' filling" of carbon granules 31" is. introduced into the chamber bounded by; the electrode. l9; closure 23-,1ringi25 and surface 29.

" Acapor-cover-Mf'crimped over the fixed electrocle closestheaperture 3 0."

The" fixed; electrode. and; rings. 25v and 26. are

securely-held in position in pile-up relation and" againstLthe 'fiange' 24 by an annular clamping band 33. one edge of which bears against an insulating disc 34 seated upon the electrode flange 28.. I

It: will be. noted that because of the difference in the forms ofth'e juxtaposed surfaces ofthe two electrodes, the spacing between these sur faces is continuously changing; specifically, in the construction illustrated, this spacing first increases, passes through a maximum, then decreases in the direction toward the diaphragm. The continuous change in curvature of the vibratile electrode surface, it has been found, substantially minimizes variations in the performance of the unit with changes in position in which the unit is held during use thereof. That is, the operating characteristics of the unit are substantially independent of the position of the unit.

Furthermore, the difference in the configurations of the juxtaposed electrode surfaces allows close spacing of these electrodes and consequently high modulation, without packing of the carbon granules.

The exact configuration of the paraboloidal surface of the electrode I9 is of some moment. Specifically, the generatrix of the surface is of the form given by the equation X =ky, where X is the coordinate normal to the common axis of the two electrodes, y is the coordinate parallel to this axis, and k is a constant. Values of 7c between 0.0563 and 0.169 have been found satisfactory.

The embodiment of this invention illustrated in Fig. 2 is similar to that shown in Fig. 1 and heretofore described. However, in the embodiment shown in the former figure, the surface 35 of the fixed electrodeis frusto-conical. One slope which was found suitable for the generatrix of this surface was of the order of 45 degrees with reference to the common axis of the two electrodes.

Although specific embodiments of the invention have been shown and described, it will be understood that they are but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims. For example, although in the embodiments illustrated the entire convex surface of the vibratile electrode is paraboloidal, a portion thereof adjacent the flange 20 may be cylindrical and the remainder paraboloidal.

Reference is made of the application Serial No. 783,324 filed October 31, 1947, of Herbert W. Bryant wherein a related invention is disclosed and claimed.

What is claimed is:

1. A telephone transmitter including a pair of electrodes having opposed surfaces bounding a chamber, comminuted resistance-varying material in the chamber and means for vibrating one of the electrodes relatively to the other, the opposed electrodes being respectively convex and concave toward the other and shaped in accordance with different geometrical formulae having different points of origin to provide a spacing between the opposed surfaces which varies continuously thereover in any phase of vibration of the one electrode.

2. A telephone transmitter comprising a fixed electrode having a plurality of surfaces of which one is a concave surface, a vibratile electrode having a convex surface of continously. changing curvature in juxtaposition to said concave surface, means including said concave and convex surfaces bounding a chamber, and comminuted resistance varying material in said chamber.

3. A telephone transmitter comprising a pair of electrodes having each a surface including a dished portion the dished portions being juxta- 4 posed, coaxial and dished in the same direction, one of said portions having a constant curvature and the other of said portions having a locus of continuously changing curvature, means for vibrating one of said electrodes relatively to the other thereof, means including said electrodes bounding a chamber of inner surface including said portions and comminuted resistance-varying material in the chamber.

4. A telephone transmitter comprising a first electrode having a concave dished portion, a second electrode having a convex surface extending toward and coaxial with said dished portion, diaphragm means coupled to the second elec trode for vibrating it relatively to the first electrode, said surface and the concave face of said portion being shaped in accordance with different geometrical formulae having difierent points of origin to provide a spacing between said surface and said face varying continuously thereover in any phase of vibration of the second electrode, means including said surface and said face bounding a chamber and comminuted resistance-varying material in the chamber.

5. A telephone transmitter in accordance with claim 4 wherein'said surface is paraboloidal and said face is substantially hemispherical.

6. A telephone transmitter in accordance with claim 5 wherein the generatrix of said surface is of the form X ky, where y is the coordinate parallel to the common axis of said face and surface, X is the other coordinate and k is a constant between about 0.0563 and 0.169.

7. A telephone transmitter in accordance with claim 4 wherein said face is frusto-conical and said surface is paraboloidal. 1

8. A- telephone transmitter comprising a pair of electrodes bounded each by a surface including a dished portion, the dished portions of the two surfaces facing each other and dished in the same direction along a common axis of revolution but of diiierently varying steepness with respect thereto wherefore the spacing between said portions is a maximum over an intermediate zone between the portions and decreases therefrom toward each electrode, means including said portions bounding a chamber, comminuted resistance-varying material in the chamber and means for vibrating one of said electrodes.

RALPH R. STEVENS.

REFERENCES CITED The following references are of record in the file of this patent? UNITED STATES PATENTS Number Name Date 2,014,427 Eaton Sept. 17, 1935 2,042,822 Bennett June 2, 1936 2,191,992 McLarn Feb. 27, 1940 2,225,488 Stevens Dec. 17, 1940 2,302,278 Voorhoeve Nov. 17, 1942 2,320,433 Herckmans June 1, 1943 2,429,988 Bryant Nov. 4, 1947 

